1. Field of the Invention
This invention relates to a method for quaternizing an amine mixture consisting essentially of disubstituted imidazolines.
2. Description of the Prior Art
Quaternary ammonium salts of compounds containing the imidazoline ring structure and further substituted in the No. 1 and 2 positions with a long chain acyclic group are recognized for their effectiveness as fabric softeners. As a matter of fact, the bulk of the currently marketed fabric softeners are of this type.
The foregoing imidazoline compounds are prepared by first condensing a higher fatty acid with a dialkylene triamine containing a secondary amine group in a gamma position with respect to at least one of the terminal primary amine groups. This condensation reaction, upon employing an appropriate amount of the fatty acid, leads to the formation of the corresponding diamidoamine which is thereupon cyclized to yield the indicated substituted imidazoline structure.
Following cyclization, the product is quaternized to provide the quaternary ammonium salts thereof using any of the known quaternizing agents for this purpose. In the commercial production of imidazolines of the foregoing type, it is not feasible from a practical standpoint to achieve complete cyclization of the amidoamine intermediate. About 92% conversion is the best that can be realized in such an operation and the inability to obtain complete cyclization presents problems in preparing the quaternary ammonium derivatives thereof.
As indicated, the cyclization product will normally contain from 8-10% primary and secondary amines. It is not feasible to exhaustively alkylate said amines in accordance with conventional quaternization practices insofar as they are prone to form mainly acid salts and thus remain as such in the final product as impurities since these compounds are devoid of fabric softening properties. Beyond this, these impurities tend to react with dyes and perfumes ordinarily present in household softening formulations thereby adversely altering the nature of these additives. In addition, there is evidence that during a quaternization procedure some of the imidazoline compounds are trapped as an acid salt by amine exchange and consequently do not react with the quaternizing agent.
The object of the present invention is accordingly that of providing a procedure for alkylating imidazoline products containing free primary and secondary amines to achieve a quaternized product having a substantially reduced amount of unquaternized imidazoline and impurities in the form of the acid salts of said primary and secondary amines.